1. The Field of the Invention
The present invention is directed generally to a high turn-down modulating burner. More specifically, the present invention is directed to a high turn-down modulating burner of the burner tube type where the burner is disposed such that its central axis is disposed vertically while in use.
2. Background Art
Prior art burners include fixed surface areas at which combustion occurs, fixed volume conductors directing fuel to fixed surface areas at which combustion occurs and are either rectangular or cylindrical in shape. The fixed surface areas may include punched holes of various diameters, slots or interwoven metallic fibers/cross-hatched sintered metal fiber. The sizes of orifices or openings through which gas mixture is supplied to the surface areas are fixed due to the fixed punched hole/slot sizes or mat density or density of fiber weaving. Therefore, given fixed surfaces areas at which combustion occurs, prior art burners are incapable of supporting combustion at a very low combustion rate. For example, when modulated to a low flow of gas, the supply of gas is insufficient to be spread across now relatively large combustion surface areas to support combustion. Therefore, prior art burners may only support a minimum heat output setting that is still quite large, even when a heating demand does not justify this setting.
In order to achieve the effect of a high turn-down at low heat output regions, burners may also be shut off periodically. Upon shut off, the amount of materials heated can drop rapidly, potentially causing discomfort to users of such materials. Cycling frequency of the burner can be also be quite high, leading to energy losses and inefficiencies caused in the need to purge during both the shut-down and start-up phases. In addition, typical start-up times for burners can be quite long, leading to an inability to respond to sudden load demands.
Thus, there arises a need for a burner capable of a high turn-down ratio and one in which the effective combustion area is adjustable to accommodate heating demands without the need to shut off burners.